It is well-known in the art of manufacturing disposable baby diapers or other sanitary disposable absorbent products such as sanitary napkins, adult incontinence pads, and hospital bed pads to provide a structure wherein the coversheet or coverstock or top sheet (i.e., that portion of the product which is in contact with a person's skin) is made of a hydrophilic material so as to be pervious to liquids, such as urine. This permits the ready pass-through of the liquid into the absorbent core or pad which lies beneath the coverstock. In the past, some coverstocks have also been made of cotton, blends of cotton and rayon, or blends of rayon with a bondinq fiber such as polyethylene.
Such coverstock, however, has been undesirable because it tends to retain the moisture and, thus, feel wet to the touch. Further, since the coverstock keeps the skin wet, it is more likely to cause a skin rash, diaper rash, or the like.
Therefore, in more recent years, it has been found desirable to use a coverstock made of hydrophobic fibers or filaments, such as polypropylene or polyester, either carded, spun-bonded, melt-blown, or the like. However, since hydrophobic material inherently tends to interfere with the pass-through of urine into the absorbent pad, it has been found necessary to treat the web with a hydrophilic-inducing material, e.g., a surfactant such as Triton X-102 distributed by Rohm & Haas Co. of Philadelphia, Pa., or MAGNASOFT manufactured by the Union Carbide Company.
The surfactant usually is incorporated with the fibers by the fiber manufacturers before being sent to the web manufacturer who forms a web which is substantially uniformly hydrophilic. A web thus formed when used as the top sheet in a baby or adult diaper is then coated in areas where perviousness is not only unnecessary but also undesirable. In a more recent form of diaper construction, a strip of nonwoven web of hydrophilic material is assembled side-by-side between two strips or webs of hydrophobic fibers. When such a 3-strip web is placed upon a diaper, with the pervious strip in the longitudinal center of the diaper, the urine can pass to the absorbent core through the center strip but not along the sides where the coverstock is impervious. However, such a pre-formed web assembled from three different materials is costly to make and more difficult to run on a diaper machine because of the seam-lines between the hydrophilic and hydrophobic strips.
Further, as described in U.S. Pat. No. 5,492,751, when non-woven laminates are made in a conventional manner, the fine fiber layer(s) (melt blown layer) has a basis weight of at least about 1.5 to 26 grams per square meter (gsm) and the continuous filament layer(s) has a basis weight of from about 5-30 gsm in order to achieve the desired softness and breathability in the laminate. Thus, the laminate would be more desirable if it were lighter weight while still having the desirable hydrophilic and hydrophobic properties. Additionally, cost benefits would be achievable in manufacture due to the need for lesser amounts of material in manufacture.
In order to overcome the above deficiencies, this invention provides a process for applying a coating material to a one-piece hydrophobic web only where the coating is desired.
Such a process is different from a padding process which applies a liquid, such as an adhesive, to an unbonded web of fibers (to create an integrated nonwoven web).
The prior art fails to teach the unique process of the present invention to produce a one-piece web with precisely located coating zones, in particular including a fine fiber layer with a melt blown content less than 1.5 gsm.